freebsd-nq/lib/libc/sys/access.2

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.\"     @(#)access.2	8.2 (Berkeley) 4/1/94
.\" $FreeBSD$
.\"
.Dd April 1, 1994
.Dt ACCESS 2
.Os
.Sh NAME
.Nm access
.Nd check access permissions of a file or pathname
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn access "const char *path" "int mode"
.Ft int
.Fn eaccess "const char *path" "int mode"
.Sh DESCRIPTION
The
.Fn access
and
.Fn eaccess
functions check the accessibility of the
file named by
.Fa path
for the access permissions indicated by
.Fa mode .
The value of
.Fa mode
is the bitwise inclusive OR of the access permissions to be
checked
.Pf ( Dv R_OK
for read permission,
.Dv W_OK
for write permission and
.Dv X_OK
for execute/search permission) or the existence test,
.Dv F_OK .
.Pp
For additional information, see the
.Dq File Access Permission
section of
.Xr intro 2 .
.Pp
.Fn eaccess
uses the effective user ID, group ID, and additional groups to authorize
the request.
.Fn access
uses
the real user ID in place of the effective user ID
and the real group access list
(including the real group ID) are
used in place of the effective ID for verifying permission.
.Pp
Even if a process's real or effective user has appropriate privileges
and indicates success for
.Dv X_OK ,
the file may not actually have execute permission bits set.
Likewise for
.Dv R_OK
and
.Dv W_OK .
.Sh RETURN VALUES
If
.Fa path
cannot be found or if any of the desired access modes would
not be granted, then a -1 value is returned; otherwise
a 0 value is returned.
.Sh ERRORS
Access to the file is denied if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EROFS
Write access is requested for a file on a read-only file system.
.It Bq Er ETXTBSY
Write access is requested for a pure procedure (shared text)
file presently being executed.
.It Bq Er EACCES
Permission bits of the file mode do not permit the requested
access, or search permission is denied on a component of the
path prefix.
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr intro 2 ,
.Xr stat 2
.Sh STANDARDS
The
.Fn access
function call is expected to conform to
.St -p1003.1-90 .
.Sh CAVEAT
.Fn Access
is a potential security hole due to race conditions and
should never be used.
Setuid and setgid applications should restore the effective uid or gid
and perform actions directly rather than use
.Fn access
to simulate access checks for the real user of group id.
.Fn Eaccess
likewise may be subject to races if used inappropriately.
.Sh HISTORY
An
.Fn access
function call appeared in
.At v7 .